>If I had to rewrite the level-1 launcher, I'd probably go for your solution, though it wouldn't be the executable itself. From what I remember, Fox keeps the .exe open, and once one user is running it, you can't rename it even if you have all the rights you want... or would it be just another error to watch for. Still, I'm not sure it would give me both "you got no rights" and "though you got rights, you can't" versions of "sharing violation" error message. How did you solve that?

I used it for a slightly different solution... I was testing to see if a file could be installed - ie if you have 20 files that need installing simultaneously it would do this trick on each file before trying anything else if it got the all clear then it would go ahead and install.
So the only error messages I had to differentiate was File in use or file cannot be renamed to itself.